Computer based harmonic simulation and testing for transformer differential relay

The effect of harmonics on the operation of a transformer differential relay is addressed. The testing facility consists of a computer-based three-phase harmonic source, programmable three-phase voltage and current amplifiers, and a digital-to-analog interface board. The software generates the harmonics and detects any trip action by the relay. Extensive experiments are performed in which the relays are subject to a matrix of distortion frequencies, magnitudes, and phases. The results of these experiments are discussed, and suggestions on the application of the relay are given